This is because local archives are close enough to allow you visit them frequently, allowing you to take the time to dig deeply and thoroughly on your chosen local subject - of which they are almost mostly likely the best single source about that local subject.
But a local subject in New York and in other world-shaking cities can frequently also be a world class subject, of interest to readers and scholars worldwide.
So, for these lucky scholars or authors , the advice gives them the best of both worlds.
But a writer in Lethbridge Alberta (population 75,000) or a grad student at Lethbridge University has a much harder go of it.
Dinosaur fossils and American Mormons, dry land farmers and oil explorers moving north pre WWI , the WWII Chemical and germ warfare range at Selkirk Alberta --- that pretty well does it , in my untutored mind, of local subjects of interest outside of a southern Alberta readership.
Halifax falls between Lethbridge and London, in terms of world shaking events at its door
Halifax Nova Scotia (population 350,000) is a near ideal harbour (for massive navies and as shelter from storms for even the largest commercial ships), conveniently midway between North Western Europe and yesterday's wealth of the Spanish Main and of today's wealth found in the hulls of Gulf of Mexico oil tankers.
(Halifax is about 2500 nautical miles or so from the offshore oil wells of Venezuela and another 2500 nautical miles or so to Plymouth England or Brest France.)
It is also in the province that is the first landfall of the twin continents of the Americas , in relationship to North Western Europe ---- so the original starting point of the historically important regular Cunard sea mail service and a key historic landing spot for early telegraph, telephone, radio signals, airplanes and now internet cables.
Controlling Nova Scotia has been damn useful for various sea empires at various times - but never really critical.
Always Halifax has just been one a dozen or so key transit points on an absolutely strategic great circle route.
So a scholar located in Halifax can tell many important stories .
Always though from the point of view of a bystander at the divisional train station like Truro NS, watching the troop trains pass through the town, en route to important action in an another continent.
But has the rise of the worldwide Internet and thus for the increasing need for all archives and data depositories to be fully accessible on the web, changed things for authors and scholars in Lethbridge and Halifax ?
Can some very important foreign historical subjects be researched while the author remains at home in their unimportant small city but still resulting in an important work because of that author's unique take on the public domain material ?
For journalism, this will never do - a visit to the site of important current event is crucial as ever , as that site (and that site only) is the place filled with eye witnesses and the physical evidence of the event.
But many authors or scholars deliberately seek to distill out what hindsight (and newly opened archives) reveals anew about long past events that were heavily censored when of contemporary interest to journalists.
Today we are all much less naive and no longer believe that powerful people and powerful organizations are not routine serial liars about events with a potential to explode all over their career, reputations , profits and re-election prospects.
The real truth is so often sordid and deeply buried in archives - not found in the sugar coated PR images of powerful people sustained while they still alive and thus able and willing to sue for libel.
This is why history-based narrative non fiction is eating into the acclaim and attention that W5 daily journalism and fictional novels once held for readers.
In the days before the Internet, there was no loss of academic quality to have a university in Dublin hold the vast bulk of the private papers of an American Nobel winning author who lived and wrote in Los Angeles.
A Montreal based scholar simply had to pony up and pay a lot to fly to visit those crucial archives - and Dublin was as about as expensive to fly to as to LA.
Yellowing seventy five year old paper was yellowing paper - in Montreal, Dublin or LA.
And the LA of 2015 does not look much like the LA of 1915 .
So yellowing photos from 1915 LA , found only in Dublin, were far more valuable for the purposes of studying this author's childhood , than seeing the actual LA (of 2015) in sound and in color and in person.
And of course today, yellowing paper is yellowing paper on the screen of a computer in Lethbridge as well as on screens in Montreal , Dublin or LA.
Reading "DIGITAL PAPER" by the always cranky Andrew Abbott reminds me that scholars in Chicago have access to the same internet as I do at home here in Halifax .
But those scholars also have enhanced access to the access-for-money portions of the internet by way of being senior professors at U of Chicago ---plus they has enhanced (because they are professors and local) access to all the material at that university's huge library and in the many libraries and archives around greater Chicago.
Their academic stature ensures access for their results in world class journals and being published in world class university presses but it also limits them in terms of what literary style they can adopt in writing their work.
They are unlikely to be able to produce scholarly work that is read both by millions of other non academics and academics outside their narrow field and by their colleagues.
The scholarly oriented non academic author still can best them in that area - and do so from Lethbridge Alberta or Halifax Nova Scotia...